Frontier AI, Frontier Engine Math, & New Models
DPO vs RLHF for Model Alignment
RLHF trains a reward model on human preferences and optimizes the policy against it; DPO skips the reward model and optimizes preferences directly. DPO is simpler and cheaper, RLHF more flexible and better studied at scale. The right choice depends on data, scale, and how much control you need over the reward.
要点
- Use DPO when you have clean preference pairs and want a simpler, cheaper pipeline.
- Use RLHF when you need a reusable reward model or online optimization against live feedback.
- Curate preference data carefully; noisy labels produce worse models than no alignment.
- Watch for reward hacking and verbosity inflation under both methods.
- Evaluate alignment separately from capability; alignment can quietly reduce reasoning.
- Keep a base model checkpoint to roll back if alignment degrades performance.
- Measure with held-out preference sets and task-specific evals, not just win rates.
- Consider variants like IPO, KTO, or ORPO when data is not clean preference pairs.
常见问题
Is DPO just cheaper RLHF?
Mostly yes in outcome, but DPO can be less stable and less controllable at large scale.
Does alignment make models less capable?
It can reduce raw capability or increase refusal; measure both before shipping.
How much preference data do I need?
Thousands of high-quality pairs for DPO; RLHF needs more plus reward-model training.
Which is safer for production?
Neither guarantees safety; both need red-teaming and evals on your policies.
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